Integration of fused glass collimated coupler for use in opto-electronic modules

ABSTRACT

An optical unit has multiple optical devices, a collimated coupler disposed relative to the multiple optical devices so that laser light can be transferred between at least two of the multiple optical devices and the collimated coupler without crosstalk, and a fused glass collimator, disposed within the collimated coupler, having multiple optical fibers arranged in a predetermined arrangement relative to the multiple optical devices so that the number of optical fibers is always equal to or greater than the number of optical devices on a use basis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC 119(e)(1) of U.S.Provisional Patent Application Ser. No. 60/302,479, U.S. ProvisionalPatent Application Ser. No. 60/302,205 filed Jun. 29, 2001, as well asU.S. Provisional Patent Application Ser. No. 60/365,489 filed Mar. 18,2002.

This application is also continuation-in-part of U.S. patent applicationSer. No. 09/896,664, and a continuation-in-part of U.S. patentapplication Ser. No. 09/896,513, and a continuation-in-part of U.S.patent application Ser. No. 09/896,196, and a continuation-in-part ofU.S. patent application Ser. No. 09/896,192, all filed on Jun. 29, 2001,as well as a continuation-in-part of U.S. patent application Ser. No.10/098,990 filed Mar. 14, 2002 now U.S. Pat. No. 6,629,780, thedisclosures of which are all incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to passive optical elements and, moreparticularly, to passive optical collimating elements.

BACKGROUND

When laser or LED light is emitted from lasers (or output from fibers todetectors or modulators), the light diffracts (i.e. it spreads out as ittravels). If that light is allowed to traverse a large distance withoutentering a fiber or being focused by a lens, it spreads out in areaquickly. If the optical devices which emit or receive this light arespaced close to one another in an array light from/to one optical devicecan mix with the light to/from adjacent devices.

FIG. 1 shows such a condition where light is output from an array oflasers and the light from each one spreads out. If the distance thelight travels in free space is long enough (typically on the order of 50micrometers based upon a typical laser-to-laser spacing (i.e. the“pitch”) of 125 to 250 microns, the light will spread out enough beforeit reaches its destination fiber such that it will mix with the lightfrom at least other adjacent devices. This is called crosstalk and itdegrades the data integrity coming from each of the devices or goinginto the fibers.

It is well known that crosstalk is undesirable. One option foreliminating crosstalk is to ensure that the fibers from a fiber cableare placed close enough to the lasers (or detectors) so that the lightreaches its destination (i.e. the fiber or device) before it spreads outtoo much.

Some optical module companies have relied on this approach.Unfortunately, most users of components want optical components withremovable cables; having to ‘snap’ in and out.

Unfortunately, a cable where the fibers come extremely close to theoptical devices provides great potential for damage the individualdevices caused by impact of an end of a fiber with a device. Inaddition, when a fiber cable is removed, the individual optical devicesare exposed to ambient environmental conditions, including humidity,which can adversely affect the lifetime of the devices.

Optical transceiver groups have been looking at 1-D arrays of opticaldevices (rather than 2-D) and have typically tried to have the opticalfibers themselves inserted so the attach very close to the devices. Theresulting yield, reliability and failure of the devices have limited theusefulness of this technique.

Others have made 1-D devices where they use a series of independentseparate fibers and attach them to a piece of silicon and then attachthe silicon to piece to a module board on which the optical devicesreside. Such pieces however, are not compatible with commercialconnectors.

Still others have made 2-D arrays of optical devices for use in digitalvideo cameras (CCD cameras). These products use what is called afiberoptic faceplate which is a fused fiber bundle where the number offibers far exceeds the number of optical devices, particularly on a usebasis. These faceplates are attached to a mounting layer right on theelectronic chip itself. With a faceplate, there is no alignment requiredbetween the optical devices and the faceplate itself since there aremany more fibers than optical devices, the light to/from the opticaldevices will pass through at least several fibers regardless ofalignment. One such example is shown in U.S. Pat. No. 5,074,683.

However, the approach of U.S. Pat. No. 5,074,683, where a piece isdirectly attached to the optical chip, forces one to constructstructures on the optical chip onto which a coupler could be placed. Theheight of such structures would be a pre-determined height and couldface tolerance errors which would limit the accuracy of heightplacement.

In addition, when coupling light into fiberoptic faceplates, becausethere are many more fibers than devices, some of the light can go into avariety of fibers and other portions of the light will miss all of thefibers and be lost. In addition, spot spreading occurs in fiberopticfaceplates which limits the efficiency of coupling.

Thus, what is needed is a way to couple light to a fiber that eliminatescrosstalk.

What is also needed is a way to encapsulate optical devices to avoidexposure to ambient conditions.

What is further needed is a way to protect the surface of the devicesfrom being impacted by fibers in a connector when it is inserted and/orremoved.

SUMMARY OF THE INVENTION

In general, we have devised a way to overcome the problems noted abovethrough the use of a fused glass fiber array integrated into anopto-electronic module.

We have also created an assembly methodology for integrating the opticalcoupler with optical device/electronic chip pieces. The integrationmethodology is broadly applicable to optical couplers made via othertechnologies.

One aspect of the invention involves an optical unit. The optical unithas multiple optical devices, a collimated coupler disposed relative tothe multiple optical devices so that laser light can be transferredbetween at least two of the multiple optical devices and the collimatedcoupler without crosstalk, and a fused glass collimator, disposed withinthe collimated coupler, having multiple optical fibers arranged in apredetermined arrangement relative to the multiple optical devices sothat the number of optical fibers is always equal to or greater than thenumber of optical devices on a use basis.

The advantages and features described herein are a few of the manyadvantages and features available from representative embodiments andare presented only to assist in understanding the invention. It shouldbe understood that they are not to be considered limitations on theinvention as defined by the claims, or limitations on equivalents to theclaims. For instance, some of these advantages are mutuallycontradictory, in that they cannot be simultaneously present in a singleembodiment. Similarly, some advantages are applicable to one aspect ofthe invention, and inapplicable to others. Thus, this summary offeatures and advantages should not be considered dispositive indetermining equivalence. Additional features and advantages of theinvention will become apparent in the following description, from thedrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a crosstalk condition;

FIG. 2A shows an example illustration of a fused fiber collimatedcoupler;

FIG. 2B shows the coupler of FIG. 2A in a “see through” form to show theinternal arrangement of the fibers;

FIG. 3 is a photograph of an end view of a fused fiber collimatedcoupler as described herein;

FIG. 4 shows one example coupler unit;

FIG. 5 shows the coupler unit of FIG. 4 after bonding and insertion of afused fiber collimated coupler; and

FIG. 6 shows the process of integrating the coupler holder piece withthe optical modules.

DETAILED DESCRIPTION

The entire disclosures of U.S. patent application Ser. No. 09/896,664,U.S. patent application Ser. No. 09/896,797, U.S. patent applicationSer. No. 09/896,513, U.S. patent application Ser. No. 09/896,196, andU.S. patent application Ser. No. 09/896,192, all filed on Jun. 29, 2001,U.S. patent application Ser. No. 10/098,990, filed Mar. 14, 2002, andProvisional Patent Application Ser. Nos. 60/302,205, filed Jun. 29, 2001and 60/365,489, filed Mar. 18, 2002 are all incorporated herein byreference. Those applications describe various techniques and devicesthat can be combined and intermixed with the present invention to formvarious novel optical apparatus including connectors, optical moduleshaving, for example, transmitters, receivers, or transceivers, andoptical communications networks incorporating such optical modules.

In general, we have devised a way to overcome the problems noted abovethrough the use of a fused glass fiber array integrated into anopto-electronic module. The fiber array acts as a collimator thatcaptures light from individual optical devices and prevents that lightfrom diffracting into the areas of adjacent devices. It also serves toprotect the optical devices from environmental conditions.

Light coupled into the fused fiber array then can be coupled into afiber bundle which has fibers arranged in an identical pattern andspacing as the fused fiber array.

We have further devised an optical coupler that holds the fused glassfiber array, accepts a fiber bearing connector, and is made to bepermanently held near the surface of the devices. It is placed closeenough to the devices to capture the light from each individual deviceto prevent optical crosstalk, yet is fixed permanently to the opticalmodule so that it is never removed and hence does not leave the devicesas vulnerable to ambient environmental effects.

Thus it will protect the devices from contact by any fibers and willencapsulate the optical devices from exposure to any ambientenvironmental conditions.

There are two separate aspects of the present invention that alone andcollectively provide advantages and benefits not present in the priorart.

First, we use a fused glass collimated coupler in an optical componentto direct or collect light near the optical devices and preventdiffraction of the light (and thus the resultant crosstalk betweendifferent optical devices to occur). The collimated coupler consists ofa series of optical fibers which are arranged in an ordered fashion,such as a grid. The fibers are arranged such that there is always one ormore devices per collimated coupler fiber on a “use basis”. As usedherein, a “use basis” means that the number of total fibers in thecoupler and the number of total devices in the module are irrelevant,even if the two connect to each other. What matters is that if only onedevice is in use it will feed only one fiber. If there are two devicesin use (in an array having two or more devices), they will either eachhave a corresponding fiber or will both have a single correspondingfiber in the collimated coupler (for example, if the two are combined bya waveguide between the devices and the collimated coupler or areredundant devices). The creation of such waveguides are described, forexample, in the incorporated by reference, commonly assigned, U.S.patent application No. entitled “Multi-piece Fiber Optic Component andManufacturing Technique”. The creation of an array of devices withredundancy is described in the incorporated by reference, commonlyassigned, U.S. patent application entitled “Redundant Optical DeviceArray”.

To make insertion and placement easier the fibers are fused togetherinto a solid block. A block of fused fibers which, when it cut to theappropriate size and has the requisite number of fibers and fiber pitch,is suitable for use as the collimated coupler and is commerciallyavailable from Collimated Holes, Inc., 460 Division Street, Campbell,Calif. 95008.

We also have separately devised a way of aligning and inserting thesecouplers into an optical module. In particular, we have devised a way toalign this collimated coupler piece to both a fiber array and theoptical devices in the module.

As noted above, the collimated coupler is made up of a series of opticalfibers which are fused together into a solid block. The fibers arearranged in a pattern, for example a square, hex, triangular, circular,etc., pattern which typically matches the arrangement of optical deviceson an optical module chip, the exception being when there are two ormore devices to a particular fiber or fibers. An example illustration ofa fused fiber collimated coupler is shown in FIG. 2A. FIG. 2B shows thecoupler of FIG. 2A in a “see through” form to show the internalarrangement of the fibers.

The fibers are fused in a fusing process which occurs during the drawingof the fibers. Each of the fibers in a bundle is drawn down so that thegroup of fibers at the end of the pulling process is the correctdiameter and on the correct pitch. The fibers fuse as the glass that thefibers are made from melts during the pulling process. FIG. 3 is aphotograph of an end view of a fused fiber collimated coupler such asdescribed herein. As shown, the collimated coupler is on its end so thatthe rows run vertical. The collimated coupler contains 7 rows of 12fibers fused together in an arrangement where the centers of the fibersare on a 250 micron pitch between fibers in a row and from row to row.

In an alternative variant, a fused fiber collimated coupler can bereplaced by a collimated coupler made of suitable size according to oneof the techniques described in the incorporated by reference, commonlyassigned, applications entitled “Multi-piece Fiber Optic Component andManufacturing Technique.”

A coupler unit is created, for example by molding out of one or morepieces a suitable resin or plastic material. FIG. 4 shows one examplecoupler unit. As shown, the coupler unit is made up of two plasticpieces, a coupler holder piece and a module connector that have beenbonded or affixed together by, for example by gluing, screwing, orultrasonically welding them together.

The non-bonded end of the coupler holder piece is constructed with arecess of suitable dimensions to accept the collimated coupler. Thecoupler holder piece has a recess of a depth such that it will clear theoptical chip when mounted and maintain the coupler at the distance thecoupler needs to be to prevent cross talk.

The module connector, on its non-bonded side is designed to accept anmating connector piece, for example, a commercial connector of the ST,LC, MT-RJ, MTP®, MPO, MPX and SMC type (MTP being a registered trademarkof US Connec Ltd.), or such other commercial or proprietary connector asdesired.

FIG. 5 shows the coupler unit of FIG. 4 after bonding and insertion of afused fiber collimated coupler.

The process of integrating the coupler holder piece with the opticalmodules is depicted in FIG. 6.

The process proceeds as follows.

1) A coupler holder piece (into which a collimated coupler can fit) isaffixed (usually permanently) to a module connector (which is thelatching piece that will sit on the module, and into which acomplementary connector can ‘snap’ in order to attach a fiber or a fiberbundle to the optical device module).

2) A Fiber Bundle Array connector, having optical fibers terminated init, is inserted into the module connector piece/Coupler holdercombination (these two pieces are designed to mate with one another).

3) (an optional step) Light is shined through the fiber bundle far endso that light emits from the fiber array connector end. This light canbe from a laser light source, an LED light source or any incoherentlight source, for example, white light.

4) The collimated coupler is inserted into the coupler holder andaligned so that the critical optical elements of the collimated couplerare aligned to the individual fibers in the fiber bundle/bundle arrayconnector. Once the two pieces are aligned, the collimated coupler ispermanently fixed in place in the coupler holder, for example with anepoxy. This assures that any time the fiber bundle array is removed fromor reconnected to the module connector that the individual fibers willstill be aligned relative to the collimated coupler.

5) The assembly containing the collimated coupler, the coupler holderand the module connector is then aligned relative to the chip assemblyso that all of the optical elements in the collimated coupler arealigned relative to all of the optical devices in the chip assembly.This assures that efficient transfer of light between the opticaldevices and the collimated coupler occurs.

6) The assembly containing the collimated coupler, the coupler holderand the module connector is then brought into close proximity to thechip assembly and permanently affixed in place. This seals the opticaldevices, ensures that the alignment between the optical devices and thecollimated coupler is maintained and ensures that the spacing betweenthe optical devices and the collimated coupler is small enough thatcrosstalk does not take place.

It should be understood that, although the above procedure was describedwith reference to the fused collimated coupler, the procedure can bestraightforwardly used with other types of collimated couplers, forexample, microlens arrays, fiberoptic faceplates used according to thedescription in commonly assigned U.S. Provisional Patent Appl'n No.60/302,205 entitled “Multi-mode Fiber Bandwidth Enhancement Using AnOptical Fiber Coupler” (filed on Jun. 29, 2001 and incorporated hereinby reference) or Provisional Patent Appl'n Ser. No. 60/365,489 entitled“Long-Throw, Tight Focusing Optical Coupler” (filed on Mar. 18, 2002 andincorporated herein by reference), diffraction gratings, waveguidedevices, etc.

In addition it should be understood that the coupler can be placedbetween a lens and an optical device to increase the “throw”. Moreover,the approach can be used to control the efficiency of the coupling byeither reducing diffraction or by deliberately causing diffraction ofhigher order modes.

Advantageously, the insertion into the coupler holder first, followed byattachment onto the electronic chip assembly not only allows aligning ofthe collimated coupler relative to the optical devices but also allowsfor the accurate control the distance between the optical devices andthe collimated coupler.

A further advantage to using the technique described herein is it allowsexact placement of the coupler as close or as far as is needed on amodule-by-module basis. The approach also ensures that the collimatedcoupler is aligned precisely with respect to any fiber bundle which isinserted.

Finally, it should be noted that the approach has applicability, notonly to active optical devices, but also to passive devices such ascoupling light to MEMS structures for all-optical networks and the likeor of coupling of elements to elements where there is a 1—1 relationshipbetween the two elements being coupled.

It should be understood that the above description is onlyrepresentative of illustrative embodiments. For the convenience of thereader, the above description has focused on a representative sample ofall possible embodiments, a sample that teaches the principles of theinvention. The description has not attempted to exhaustively enumerateall possible variations. That alternate embodiments may not have beenpresented for a specific portion of the invention, or that furtherundescribed alternate embodiments may be available for a portion, is notto be considered a disclaimer of those alternate embodiments. One ofordinary skill will appreciate that may of those undescribed embodimentsincorporate the same principles of the invention and others areequivalent.

What is claimed is:
 1. An optical unit comprising: multiple opticaldevices; a collimated coupler disposed relative to the multiple opticaldevices so that laser light can be transferred between at least two ofthe multiple optical devices and the collimated coupler withoutcrosstalk, and a fused glass collimator, disposed within the collimatedcoupler, comprising multiple optical fibers arranged in a predeterminedarrangement relative to the multiple optical devices so that the numberof optical fibers is always equal to or greater than the number ofoptical devices on a use basis.
 2. The unit of claim 1 wherein themultiple optical devices are arranged in an N×M array.
 3. The unit ofclaim 1 wherein the predetermined arrangement is a rectangular array. 4.The unit of claim 1 wherein an optical fiber of the fused glasscollimator is coupled to at least two of the multiple optical devices.5. The unit of claim 1 wherein at least two of the multiple opticaldevices are lasers.
 6. The unit of claim 5 wherein another of the atleast two optical devices is a detector.